Description:
We report atmospheric methane carbon isotope ratios ($\delta^{13}CH_4$) from the Western Greenland ice margin spanning the Younger Dryas-to-Preboreal (YD-PB) transition. Over the recorded ~800 years,$\delta^{13}CH_4$was around -46 per mil ($\textperthousand$); that is,$\sim 1\textperthousand$higher than in the modern atmosphere and$\sim 5.5\textperthousand$higher than would be expected from budgets without$^{13}C-rich$anthropogenic emissions. This requires higher natural$^{13}C-rich$emissions or stronger sink fractionation than conventionally assumed. Constant$\delta^{13}CH_4$during the rise in methane concentration at the YD-PB transition is consistent with additional emissions from tropical wetlands, or aerobic plant CH4production, or with a multisource scenario. A marine clathrate source is unlikely.